Indoor and outdoor air pollution are major global contributors to human disease, disability, and mortality. Household air pollution, which, in developing countries, results primarily from the incomplete combustion of primitive fuels for cooking and heating (e.g., wood, charcoal, etc.), is considered the 6th leading risk factor for disease and death on the planet. Outdoor air pollution from particulate matter, which results primarily from the combustion of fossil fuels for power generation and transportation, is considered the 11th leading risk factor.
Despite these alarming statistics, current understanding of human exposure to air pollution (whether indoors or outdoors) is limited. Although regulatory agencies such as the U.S. Environmental Protection Agency maintain national air quality monitoring networks, the monitors underlying these networks tend to be relatively sparse, costly to maintain, and report only outdoor pollution levels. Furthermore, data from such monitoring networks only modestly correlate with an individual's daily exposure to air pollution. Since the vast majority of people spend their lives indoors, moving from one microenvironment to the next (e.g., at home, at work, or in transit), assessment of personal exposure remains the standard for determining individual risk. Studies that have examined personal exposure to air pollution, however, have consistently demonstrated lognormal variations in exposure that span both space and time. Characterizing lognormal exposure distributions requires studies with relatively large sample sizes; however, most of these studies are limited to modest sample sizes because of limitations in the technologies used to assess personal exposure.
A major constraint on the current ability to assess personal air pollution exposure is the cost and physical burden of the monitors themselves. For monitoring exposure to particulate matter (PM), personal air samplers typically consist of a battery-powered diaphragm pump connected by tubing to a size-selective inlet (e.g., a cyclone or impactor) to measure inhalable, respirable, or PM2.5 size fractions of particulate matter within the wearer's breathing zone. Such personal air samplers are expensive (typically costing >$1500 each), relatively heavy (>0.5 kg in total), and noisy (emitting >60 dB from the pump). The physical burden posed by these monitors (noise, visual aesthetic, and weight) make them difficult to wear for extended periods. Further, the diaphragm pumps must be periodically checked for flow accuracy and the tubing connections often disconnect or become pinched if the wearer is physically active. For these reasons, studies of personal PM exposure often suffer from small sample size and data loss due to poor user compliance and instrument reliability.
Historically, the development of PM exposure monitors was driven by the need to assess occupational intake for aerosol hazards in the dusty trades such as mining, construction, manufacturing, and agriculture. In those workplaces, the weight and noise of the monitors was less of a hindrance. For personal monitoring among the general population (or outside of heavy industry), however, a need exists for technology that overcomes these limitations. Therefore, there is a need for a wearable and portable air pollution monitor to address the numerous limitations of currently available monitors, without sacrificing precision, accuracy, and reliability.